The present invention relates generally to information networks, and more particularly, to the configuration and operation of an optical network.
In an optical network, it is essential that each network element be able to transport a large number of optical signals that may have varying power levels. This is required because signal power levels dynamically change as signals are switched and routed throughout the network.
In a two fiber optical bi-directional line-switched ring (OBSLR) network, working and protect channel pairs are routed around the network. As a result of network switching events, the working and protect channels may be routed on different signal paths, with each signal path having a different loss characteristic. Thus, it is possible that at any given point in the network, a working and protect channel pair can have different signal power levels. This situation can result in increased bit error rates (BER) on the lower power channel.
FIG. 1 illustrates how path variations due to typical network switching events can result in power level variations between working and protect channel pairs. A working path contains two channels, 1 and 2, with individual channel power of A as shown at 102. The protect path has two channels, 3 and 4, with individual channel power of A as shown at 104. In a typical system, the working and protect channels may be routed via different signal paths that have different signal loss characteristics. As a result of the different routing paths, the working and protect channels may have different signal power levels at some point in the network as shown at 106. For example, after being routed via one path, channels 1 and 2 have channel power of B; and after being routed via another path, channels 3 and 4 have channel power of C. After being multiplexed together, the channels still maintain their respective channel power levels, and have a power level differential as shown at 108. The power level differential 108 between the working and protect channels may result in excessive BERs, since the lower power channels may have a signal level that is too low to be adequately transmitted and received on the network.
In addition to the signal loss associated with different routing paths, the power level differential 108 between the working and protect channels may increase when the signals are amplified. For example, the aggregate channels, as shown at 106, may be input to an amplifier that experiences saturation effects caused by the relatively high power level of channels 1 and 2. The saturation effects may result in non-linear amplification which may increase the amplitude differential 108 to cause the resulting amplified signals to appear as shown at 110. Due to the saturation effects of the amplifier, channels 1 and 2 receive greater amplification than channels 3 and 4. Thus, channels 1 and 2 have channel power of D, and channels 3 and 4 have channel power of E. The resulting increased power level differential is shown at 112. This large power differential contributes to increased BERs as the signals are further switched and transmitted around the optical network.
In typical optical networks, each node may be manually configured to operate in accordance with intended signal routing in the network. For example, preset attenuation pads, having a fixed attenuation value, are inserted in signal transmission paths to set signal attenuation around the network.
In addition to the problems associated with path loss and amplifier saturation, manually configuring each node in an optical network presents a number of additional problems. First, manually configuring each node is prone to errors. Thus, if a node is configured improperly, it must be manually reconfigured again thereby adding costs. Second, each node must be engineered per site. This means that the nodes are not identically configured, and therefore each node must be customized. Third, it is difficult to upgrade any network components. For example, upgrading a component in a node may affect other components in the node. Changing a node may affect adjacent nodes. Thus, upgrades and maintenance for manually configured networks is difficult and expensive. Fourth, it is difficult to add nodes to an existing network, since the added node and each node it affects must be manually configured. For example, manual configuration may require nodes to be added in a specific sequence or introduce a limitation on the number of new nodes that may be added. Finally, the network may become unstable if due to signal routing or switching events, the signal levels are not as anticipated when the manual configuration occurred. For example, if signal power levels change as a result of a network switching event, the initial manual configuration of a network element may result in that element being unable to handle the new signal power levels.
The present invention provides a system for managing signal power levels in an optical network. In one power management strategy provided by the invention, a consistent output power per wavelength is maintained between neighboring network elements in a OBSLR network. Consistent means that the signal power level between network elements will not change significantly enough, over any switching condition in the network, to affect the ability of the network to carry traffic. This localizes power management within each node since input power levels to the nodes remain constant. As a result, power management for the network becomes a function of each node""s internal component configuration and optical path variations. In this strategy all switching scenarios are folded into a small set of operating modes.
In another power management strategy provided by the invention, signal power parameters for different network switching scenarios are tracked. Thus, it is possible to optimize the available signal-to-noise ratio (SNR) in the network at the cost of calculating, storing and exchanging signal power parameters around the optical network.
In another power management strategy provided by the invention, signal power parameters for different network switching scenarios are pre-computed and stored. The pre-computed values provide a way for network elements to quickly react to switching events without necessarily having to re-compute parameters as each event occurs.
In an embodiment of the present invention, a method for managing signal power levels in an optical network is provided. The optical network comprises a plurality of nodes having logic to receive and transmit optical signals over a plurality of network interconnections. The method comprising steps of: providing each of the nodes configuration parameters; configuring each of the nodes based on the configuration parameters; exchanging power parameter information between the nodes; re-configuring at least some nodes based on the power parameter information; and repeating the steps of exchanging and re-configuring until the optical network is fully configured so that the optical signals have selected signal power levels.